MAKING a high-quality MIG weld is no easy task. But making a high-quality MIG weld when your gun and consumables aren't functioning properly is just about impossible.
Porosity, excessive spatter, undercut and burn back are just a few of the problems that can occur when something's not right with these components. Troubleshooting weld defects can be a difficult task, since any single problem can be caused by a variety of factors.
It is often easier to avoid weld defects from occurring by conducting a thorough check of your MIG gun and consumables prior to welding than it is to troubleshoot an existing issue. Problems will inevitably occur, however, and being able to quickly and accurately identify their source will save you both money and frustration.
The following is a guide to solving many of the most common consumables and gun-related problems associated with MIG welding.
Wire does not feed — There are a number of problems that could cause the wire to not feed, including issues related to the feeder relay, control lead, adapter connection, liner or the trigger switch.
Begin troubleshooting this problem by checking whether the drive rolls are turning when the gun trigger is pulled. If they are not turning, an electrical continuity failure is occurring. Check the terminals and connector contact pins to ensure the gun is properly connected to the wire feeder. The wire can also fail to feed if the trigger switch is broken, or control leads in the gun cable are damaged. If this is the case, they will need to be replaced.
If the drive rolls are turning but the wire is not feeding, it is usually caused by inadequate drive roll pressure or a blockage in the contact tip or liner. Check the drive rolls and contact tip before moving on to the liner, which takes more time and effort to check and replace.
If a faulty feeder relay is the cause, consult the feeder manufacturer for information on correcting the problem. A broken control lead or a poor adapter connection will require you to test and replace the leads and/or contact pins. Some guns feature a spare set of control leads that can be used to correct the problem. With others, it may be necessary to replace the entire cable.
Contact tip burnback — While burnback (see photo) will occur from time to time even when there isn't anything wrong with your gun and consumables, it could also be caused by improper equipment set-up. Be sure to check the following factors if you experience an increase in your contact tip burn back rates.
Improper tip recess and improper wire stick out can cause increased burnback frequency. In the case of incorrect tip recess (or stick out), you will need to install a nozzle and tip combination with a different recess. Similarly, adjusting the distance between the gun and the work piece (tip-to-work distance) will resolve burnback problems associated with wire stick out.
A faulty work lead/ground is another possible cause of burnback. Check and possibly replace the electrical connections and cables to ensure a faulty work lead/ground will not cause any further burnback.
Erratic wire feeding, a problem with several possible causes, is a frequent source of burnback. See the section below for information on correcting erratic wire feeding.
Erratic wire feeding — Erratic wire feeding simply means that the wire is not feeding from the gun at a consistent rate. This problem is usually caused by the liner, the drive rolls or the contact tip.
A worn out or kinked liner, or build-up of debris, filings, dirt and other foreign material inside the liner, the wrong size liner and gaps at the liner junctions caused by an improperly trimmed liner can all cause the wire to feed erratically. In each case, the liner will likely need to be replaced and properly trimmed so that it fits as tight as possible to the other components.
Improper drive roll size, worn out drive rolls and improper drive roll tension are also potential causes of erratic wire feeding. Replace worn out drive rolls or those of the wrong size with correctly sized and tensioned drive rolls.
Another common cause of erratic wire feeding is a contact tip that is worn out or the wrong size for the wire being used. If you suspect the contact tip is causing the wire to feed erratically, it is best to replace the tip.
Short contact tip life — Although quality plays a critical role in contact tip service life, tip life can vary dramatically from application to application, and it is difficult to give an average longevity to expect from your tips. If you notice a change in your contact tip life from their normal life spans, however, check and replace the following factors as necessary.
Using the wrong size contact tip, exposure to excessive heat or erosion caused by the wire are all contributing causes to premature contact tip degradation.
If your contact tip is melting due to excessive heat, it is likely a result of exceeding the product's rated amperage or duty cycle, in which case you should replace either the tip or the tip and the MIG gun with heavy-duty equipment.
If the wire is prematurely wearing out the contact tip, the drive rolls may be creating small burrs on the wire that can erode the inside of the contact tip (see photo). Setting the drive roll tension too high can also create deformities in the wire that cause it to mechanically wear out the tip, which is especially common with knurled drive rolls. If this is the case, the drive rolls will need to be properly tensioned or replaced.
The wire can also cause premature contact tip failure if it is rusty, dirty or simply a low quality wire with excessive imperfections. If this is the case, the wire needs to be replaced.
Erratic arc — If not caused by erratic wire feeding, the most common cause of an erratic arc is usually inconsistent electrical conductivity. If the contact tip is either too big to begin with or worn out from use, it can fail to consistently conduct electricity to the wire and thereby cause an erratic arc. In either situation, the contact tip should be replaced with a new one that is the correct size.
If the gun neck being used is too straight, it could produce an erratic arc through a lack of conductivity. The bend in the neck increases electrical conductivity by creating a continuous contact point as the wire is guided along the outside of the bend in the liner and through the tip. An erratic arc caused by an insufficient bend angle needs to be addressed through the installation of a neck with a 45- or 60-degree bend. Another possible cause of an erratic arc is a worn or kinked liner, or build-up inside the liner, which should be resolved by replacing the liner and checking the condition of the wire to ensure there are no inconsistencies that will cause the problem to recur.
Also be sure to check the work lead/ground clamp and gun connections to ensure a good electrical circuit is established.
Extreme spatter — From a gun and consumables perspective, improper tip installation and improper weld puddle protection are two common causes of excessive spatter (see photo). First check to make sure the tip is installed properly and that it is at the correct recess for the application.
Next, verify that the correct shielding gas is being used and that the weld is receiving adequate shielding gas coverage. Too little or too much shielding gas can both cause poor weld puddle protection and lead to excessive spatter. Clogged nozzle and diffuser orifices could cause too little shielding gas flow, so check and clean or replace the nozzle and diffuser as necessary.
Additional non-equipment-related causes of excessive spatter can be incorrect electrical parameters or a contaminated work piece. Verify that the voltage and wire feed speed are at the recommended levels for the application and that the work piece is free of rust, mill scale and other contaminants.
Some welding factors, such as the short circuit process, using pure CO2 gas and galvanized metal have inherently higher spatter rates, which can be mitigated through using an Argon rich gas blend or a different filler metal transfer process.
Porosity in weld — Porosity, which are holes in the weld bead caused by trapped contaminants and gasses can have many causes (see photo). Exposure of the weld puddle to atmospheric air, whether as a result of plugged gas ports, a ruptured gas hose, too much or too little gas flow, or a faulty solenoid, is one of the most common causes of porosity. Ensure proper gas flow before moving on to diagnose other possible causes of porosity.
Worn out or damaged parts, including the diffuser, the insulator, o-rings and fittings can all lead to compromised gas coverage. Check each of these components and replace as necessary. Further causes of porosity include excessive wind in the welding environment blowing away the shielding gas, in which case you will need to either move to a less windy site or set up screens to block the wind.
Gun running hot — If your gun is getting too hot, it is most likely because you are either exceeding its rated amperage or duty cycle, or else loose power connections or a degraded power cable are causing excessive resistance in the weld power circuit. If you exceed the gun's duty cycle, you can either decrease the parameters to within the gun's rating, or use a higher rated gun.
If loose connections are causing the problem, clean and tighten connections that are in good working condition or replace ones that are worn out. One common symptom of loose power connections or a degraded power cable is a discolored liner (see photo). The discoloration is caused by heat and indicates that weld current is being carried through the liner instead of the gun's power cable. Also check to make sure the work lead/grounding connection is tight and free of obstruction.
Although it's clear from the above problems that there are many ways that your MIG guns and consumables can lead to poor weld quality, the good news is that most problems usually have simple and inexpensive solutions. By following these recommendations, you will be able to address and resolve the vast majority of the most frequently encountered welding problems.
For more information on troubleshooting specific welding problems, contact your nearest welding distributor or the customer service department at the equipment manufacturer.